Load limiting damper



May 30, 1933. A. E. SEELIG 1,912,164

LOAD LIMITING DAMPER Filed March 14, 1951 Tiqi.

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A; ATTORNEY Patented May 3Q, 1933 -UNITED STATES ALFRED E. SEELIG, or new YORK, n. Y., ASSIGNOR 'ro L. J. WING MFG 00., roan, n; Y., A CORPORATION or NEW YORK PATENT OFFICE LOAD LILIITING DAMPER Application filed March 14,1931. Serial No. 522,604.

This invention relates to damping devices for controlling the volume of air delivered by propeller tans located in a conduit, usually cylindrical, and rotated about an axis 5 substantially coincident with the axis of such conduit.

7 When a propeller fan is rotated in a conduit, of approximately the same diameter as the fan, the volume of air delivered should 10 theoretically be determined by the product of the pitch of the blades of the fan, the rate at which thefan'is revolved and the area of the'conduit. In practice, the amount of air delivered is always less than such theoretical amount as the higher pressure on the delivery side tends'to produce a flow of air between the fan blades near the center in a direction opposite to the direction of flow induced by the rotation of the an blades. Asthe pressure onthe delivery side of the fan rises, the volume of air delivered by the fan becomes less and less until finally the rate at which air flows back nearfthe center becomes equal to the rate at which 2 air fiows forward near the periphery and air flow ceases so that the fan produces a circulation of air in its immediate vicinity but no ,delivery of air from thedischarge end of the conduit. As the air flow away from the fan is progressively restricterhthe pressure'on the delivery side of the tan between the latter and the point of.restrictio11 increases and causes'a corresponding progressive diminution in the volume otthe air delivered by the fan.

The increase in, pressure on the delivery side of the fan produces an increasing resistance to the rotation of the latter, and,

0 hence, as the delivery pressure increases, there is a proportional increase in the power required to drive the fan at constant speed. From this it follows that the greater the "extent to which air flow is restricted the greater the power required to drive the fan. 1 The volume of air delivered may be va ried either by changing the speed of rotation ot' the fan or by maintaining the speed of rotation constant and restricting'theflow of air from the fan." Adjustable speed motors operating at high speeds have not been found as satisfactory and as reliable as constant-speed motors, and the present invention is more particularly designed for the regulation of blowers driven by electric motors of the constant-speed type. Withfans of the propeller type the horsepower required to rotate the fan at constant speed increases as the resistance tothe air flow increases'upto the point atwhich air flow entirely ceases. Hence, when applying dampercontrol for the regulation'oii the air supplied by propeller fans when operated with constant-speed motors, it becomes necessary to use motors of much larger capacitythan is required for any of the usual points of operation. due to the factthat the complete closing of the damper would overload a motor selected to meet the requirements of the ordinary resistance of the air passages of the system being supplied with air, as for example, in the fuel bed ofa coal- Heretofore, the air-controlling means conduit in which'the fan is located. 4 v

It is an object of this invention'to so construct the damper as to-limit the maximum load that can 'be put on the motor, thus making it possible to employ a constant speed motor of lower-capacity and smaller weight and dimensions, and'yet secure regulation ofair flow suflicient for many practical purposes.

According to the present invention,'the air flow controllingor damping means are constructed'so that theyareincapable of reducing or throttling the flow of airbelow substantial fraction of the fiow with the dampingmeans in fully 'open position. As the size offthe fan motor is determined by the load on the fan with the damping means in position of maximum throttleftlie motor may be considerably smaller than is the case with dampingmeans .capableof entirely closing the air conduit.

j Further, I have found that the power required to drive a propeller fan at constant full capacity speed under restricted flow in which the air flow is restricted. The volume of air delivered by the blower is usually regulated by adamper arranged in the conduit on the delivery side of the fan and consisting'of a disc of the same diameter as that of the conduit, which disc may beturned about its diameter from a position parallel to the direction of flow to one perpendicular thereto. l

A dampen disc of such form operates by restricting the flow of air along the center of the conduit and allows unrestricted flow adjacent the periphery Ihave found that if conditions are reversed, i. e., if the flow of air at the periphery is restricted and the flow of air at or near the center is unrestricted,.the power required to operate the fan at constant speed but with reduced air output as the damper is progressively closed is much. .less by comparison. This result is obtained in spite of the fact that a propeller type of fan prcducesa flow of air in the conduit having a much higher velocity near the periphery of the conduit than adjacent the center.

I cannot give the exact reasons why a damper acting on the peripheral high velocity air currents instead of the center low velocity air currents increases the fan delivery pressure, and, hence, the power required to operate the fan, less than a damper acting in .the reverse. manner. It is, however,an established fact and has important results. Dampers'constructed in accordance with the present invention not only reduce the .power required to operate the fan under throttled conditions, but also enable smaller motors to be employed. The size of the motor is determined by the maximum load, and this is reduced by the use of the new and improved damping method.

The relation of pressure differences to the damping means, involves questions of location of thedamping means. As a general rule, flow of air to the fan is of more uniform velocity than flow away from the fan, that is, there is less. difference in air velocities at the-periphery and center of the conduit on the intake than on. the delivery side'of thefan. There is a difference, however, as the suction of the fan is greatest at its periphery. Tlhen, the further the damper is located fromthe fan, the less difference there is between the peripheral and central air velocities. The greatest advan- -tages of the present method of damping are,

therefore, obtained with the damper arranged as near the fan as possible on thedelivery side. The advantages will also be obtained to a lesser degree with the new form of damperlocated near the fan on the intake ,side' or at a little distance from thefan on the delivery side. Best results .are ordinarily obtained when the damper fire-box of a boiler or the like. box comprises-side-walls 5, 5, and grate bars in closed position is not spaced away from the forward or. delivery edges of the fan blades a greater distance than the outside diameter of the fan, preferably not more than one-quarter or one-half that distance.

Exceptv where unusual conditions require greater spacing, the damper should not be further from the fan than twice the diam eter of the latter.

--I have also found, using my annular form of damper, that if the conduit is completely blocked at a distance from the fan, the power consumed by the latter is very considerably greater .whenthe damper is full open than when the damper is closed. Presumably the closing of the damper produces acirculation of air from the periphery of the conduit towards the center of the fan which prevents the building upof excessively high delivery pressures by allowing escape of 'air between the blades near the center of the fan.

The central aperture in the damper isusually of considerable size with respect to the outside diameter. For most purposes, the area of the central aperture should not be less than one-quarter of the cross-sectional area of the conduit at that, point, and frequently the desired regulation is obtained when thearea of the central aperture is half not inaction. A damper of this latter type f of construction is illustrated, by way of example, in the accompanying drawing, where- 1n:-

Fig. l is a vertical section through a firebox provided with a propeller fan and damper to supply a regulatableamount'of air thereto.

Fig. 2 is a detail sectional view on the line 2-2 of Fig. 1.

Fig. 3 is' a detail sectional view on the line 3-3 of Fig. 1.

The improved form of'damper is shown as applied to the regulation of air tothe The fire- (Sadapted tosupport a bed of fuel 7. In

one of the side-walls below the gratewbars is located a conduit 8 of circular CI'OSS-S8C- tion. In front of the outer opening of this conduit is mounted an electric motor 90f the constant speedtype. A fan 10 is mountside of the fan. The damper, as above stated, may be constructed in various ways, one convenient form of construction comprising, as illustrated, two semi-annular portions 11, 11, each rotatably mounted on shafts l2 and 12a, journalled in the walls of the conduit. Any convenient means for opening and closing the damper may be employed. Advantageously, however, the two portions of the damper are interconnected for simultaneous operation. For this purpose the shafts 12 are arranged to project upwardly into a chamber 13 in the wall 5. Slidably mounted in this chamber is a bar 14 having rack teeth 15 on either side for engagement with pinions 16 secured to the upper ends of the shafts 12. By moving the bar 14 longitudinally the pinions 16 may be rotated to open and close both portions of the damper simultaneously. The movement of the bar 14 may be automatic or manual, as shown. For manual control the bar projects outwardly from the chamber 13 and is provided with a handle 17.

As shown in full lines in Fig. 3, the damper is in about half open position. The dotted lines in that figure show the closed position of the damper. It will be noted that in closed position the damper is spaced away from the delivery edges of the fan blades a distance less than half the diameter of the fan. The area of the central aperture in the damper is somewhat greater than one quarter of the area enclosed by the periphery of the damper or, what amounts to the same thing, the inside diameter of the conduit at that point.

It is understood that numerous changes may be made in the form of damper, its location, mode of operation and control without departing from the spirit of this invention. For instance, where an annular damper is used, the opening in the damper may be square, annular, multiple, or any desired form.

What I claim is:

1. The combination of an air conduit, a propeller-type fan revoluble therein about an axis substantially coincident with the axis of the conduit, means for driving said fan, and adjustable damping means in said conduit near said fan on the delivery side thereof adapted to retard the flow of air in said conduit to a greater extent adjacent the periphery thereof than at points nearer the center.

2. The combination as in claim 1, in which the damping means are spaced away from the fan not more than twice the outside diameter of the fan.

3. The combination as in claim 1, in which the damping means are spaced away from the fan not more than the outside diameter of the fan.

4. The combination as in claim 1, in which the damping means are spaced away from the fan not more than half the outside diameter of the fan.

In testimony whereof, I have hereunto set In hand.

y ALFRED E. SEELIG... 

